1. Field of the Invention
The present invention relates to a hybrid induction motor, and more particularly, to a hybrid induction motor having a reverse rotation preventing function.
2. Description of the Background Art
In general, an induction motor includes a stator forming a rotating magnetic field and a rotor unit rotatably disposed from the stator with an air gap therebetween. Recently, the so-called hybrid induction motor, which has a permanent magnet interposed between the stator and the rotor unit, has been widely used so as to enhance operational efficiency and reduce power consumption.
FIG. 1 is a cross-sectional view of a conventional hybrid induction motor, and FIG. 2 is a cross-sectional view of a cage rotor portion taken along line II-II of FIG. 1. With reference to FIG. 1, the hybrid induction motor of the prior art includes: a housing 151, a cover 155, a stator 110 and a rotor coupling body 120 rotatably received in the stator 110.
The housing 151 is a container having an opening at its front side, and the cover 155 for covering the opening is coupled with the front side of the housing 151.
Bearing receiving portions 153 and 157 capable of receiving bearings 125, respectively, are formed at a rear side of the housing 151 and a center portion of the front side of the cover 155.
The stator 110 includes a stator core portion 111 and a stator coil portion 115.
The stator core portion 111 is formed by insulating/laminating a plurality of electric steel sheets, each having a rotor receiving hole 112 and a slot 113 formed thereon.
The stator coil portion 115 winds around the stator core portion 111 and generates a rotating magnetic field.
The rotor coupling body 120 includes a rotary shaft 121, a cage rotor portion 131 integrally coupled to a circumference of the rotary shaft 121 so as to be rotatable, and a permanent magnet rotor portion 141 coupled to a circumference of the cage rotor portion 131 with a certain air gap so as to be rotatable with respect to the rotary shaft 121.
The bearings 125 are insertedly installed in the bearing receiving portions 153 and 157, respectively, and support the rotary shaft 121 so as to be rotatable. A fan 150 is coupled to a front end of the rotary shaft 121.
The permanent magnet rotor portion 141 includes a permanent magnet 142, and a magnet support portion 144 having one side coupled with the rotary shaft 121 so as to support the permanent magnet 142 to be rotatable and the other side integrally coupled with the permanent magnet 142.
With reference to FIGS. 1 and 2, the cage rotor portion 131 includes: a rotor core portion 133 formed by insulating/laminating electric steel plates, each having a shaft hole 134 at its center and a plurality of slots 135 along a circumferential direction; a conductor bar 137 disposed inside each slot 135; and an end ring portion 139 formed to electrically connect both ends of the conductor bar 137 to each other.
Hereinafter, the operation of the conventional hybrid induction motor illustrated in FIGS. 1 and 2 will be described.
A rotating magnetic field is formed if power is supplied to the stator 110.
The permanent magnet rotor portion 141 performs relative rotation to the rotary shaft 121 so as to correspond to the rotating magnetic field and is synchronized.
An induced current flows through each conductor bar 137 of the cage rotor portion 131 by a magnetic force of the permanent magnet rotor portion 141, and accordingly the cage rotor portion 131 is rotated integrally with the rotary shaft 121.
However, the conventional hybrid induction motor has a problem that the permanent magnet rotor portion 141 and the cage rotor portion 131 rotate reversibly because of a voltage phase at the first power input, an influence of an unbalanced rotating magnetic field and initial polarity of a magnet or the like.
Accordingly, in order to prevent such reverse rotation, the conventional hybrid induction motor requires a separate reverse rotation detecting and blocking circuit (not illustrated), which thusly increases the manufacturing cost.